1. Field of the Invention
The present invention relates to a backlight module, and more particularly, to a backlight module and an LCD using the backlight module.
2. Description of Prior Art
With a rapid development of monitor types, novel and colorful monitors with high resolution, e.g., liquid crystal displays (LCDs), are indispensable components used in various electronic products such as monitors for notebook computers, personal digital assistants (PDAs), digital cameras, and projectors. The demand for the novelty and colorful monitors has increased tremendously.
Backlight modules are one of key components of liquid crystal display panels (LCD panels). Liquid crystals do not emit light, so backlight modules provide an evenly distributed light source providing abundant brightness. The light source is transformed into a high-brightness planar light source having a uniform luminance distribution via a simple, effective opto-mechanism to provide LCD panels with a backlight source. LCD panels have been extensively employed in electronic devices having growth potential, such as monitors, notebook computers, digital cameras, projectors, etc., and particularly in large-sized panels like notebook computers and LCD monitors. Thus, demand for backlight units is growing gradually as well.
In addition to cold cathode fluorescent lamps (CCFLs), backlight modules also use light emitting diodes (LEDs) as a light source. LEDs have become the mainstream backlight source for LCD televisions in recent years, because they are mercury-free and thus environmentally-friendly. In addition, LEDs respond fast. Current LEDs are mostly driven by a direct current (DC). But, since LED lighting gets gradually popular, alternative current (AC)-driven LEDs have been more and more common as well. The advantage of AC-driven LEDs is that LEDs only turn on and off in half of the time during an entire circuit period; it greatly reduces heat dissipation from LEDs and further prolongs life of LEDs. For AC-driven LEDs under ideal operating conditions, current limiting resistors have to be connected in series with LEDs to limit the amount of current flowing through the LEDs. But, the conversion efficiency of the circuit may be thus lowered due to a voltage drop caused by the current flowing through the LEDs.
A reduction in the number of current limiting resistors may cause LEDs to be burnt out easily. AC voltage fluctuations vary with different areas and environments, and LED forward voltage (VF) changes with temperature and technologies of manufacturers. Thus, problems like the burn-out of LEDs or the brightness inadequacy of LEDs may occur if the number of current limiting resistors is deliberately reduced or the resistance is deliberately lowered for increasing efficiency.